I think healers in general is going to be an odd one for getting opinions, because you're definitely going to get mixed opinions and some divide. My general advice with anything is to try it and see if you like it. A hundred of us could post in here saying how terrible it is and the moment you pick it up you might go "hey, this is fun, I like this" and our points would be moot. Many of us have fallen in love with our healers at different points in their life cycle and thus have gotten different things out of it. As an example for me, a lot of the SMN community doesn't like 5.0 SMN for how it feels to play. Me? I mostly like it, so in a way I found myself going against popular opinion. Whereas with SCH I hate it now.

New AST? I didn't play much of old AST to be connected to how it used to play. Though I am fully aware of why not everybody likes it and why it's less popular right now and would not want to downplay that.

But out of the 3 healers at the moment, despite it being the least popular, I've been enjoying AST the most, though not without its problems. But there's more to do and less downtime versus the other healers (at least in Noct Sect, which I mostly play in, simply because it is the weaker of the two). As odd as it sounds, I feel at times either healers heal too well or the content is not challenging in the right way for us to fully use our toolkit (and I think they all have a good toolkit), so with Noct being weaker, it feels like I get to use more of it.

The good news for somebody newer to healing in this game is that you will likely feel there to be less of an issue with downtime (unless you're a natural at it, I guess), though there may become a point where it does. Because as with anything there's a learning curve. Those of us who have healed in this game's content the longest are probably going to be the most disatisfied.

However, when it does come to downtime, out of the 3 AST actually has the most to do, AST cards make up for a part of your activities between DPSing and healing, which the other 2 healers don't have. But in terms of balance, it is behind WHM and SCH on every front. In terms of fun, entirely subjective of course. It depends on what you're looking to get out of your experience.